An AC-driven surface discharge PDP having a three-electrode structure is known as a PDP suitable for a full color display using three color phosphors.
FIG. 9 is a schematic cross-sectional diagram showing a structure of a common AC-driven surface discharge PDP.
The PDP shown in the drawing comprises a front glass substrate 1 and a rear glass substrate 5, which are disposed parallel to one another. Formed on the front glass substrate 1 are display electrodes 2 that are covered by a dielectric glass layer 3 and a magnesium oxide (Mgo) dielectric protective layer 4 (see, for example, Patent Reference 1).
On the rear glass substrate 5, on the other hand, address electrodes 6 and barrier ribs 7 are disposed, and phosphor layers 9-11 of respective colors (red, green, and blue), which are composed of oxide phosphors, are each provided in the space between two adjacent barrier ribs 7.
The front glass substrate 1 as formed above is disposed on the barrier ribs 7 arranged on the rear glass substrate 5, and discharge gas is filled between these substrates 1 and 5 to form a discharge space 8.
In this PDP, vacuum ultraviolet light (predominantly, a wavelength of 147 nm) is generated through an electric discharge, and the phosphor layers 9-11 of three colors are excited to thereby emit light, which results in a display in colors.
The above PDP can be manufactured as follows.
A silver paste is applied to the front glass substrate 1, and then fired to form the display electrodes 2. Further, a dielectric glass paste is applied over the display electrodes 2, and then fired to form a dielectric glass layer 3, on which a protective layer 4 is formed.
Onto the rear glass substrate 5, on the other hand, a silver paste is applied and fired to form the address electrodes 6. Next, a glass paste is applied at predetermined intervals, and then fired to form the barrier ribs 7. Subsequently, the phosphor layers 9-11 are formed by respectively applying phosphor pastes of individual colors to the spaces between the barrier ribs 7, and firing the phosphor pastes at around 500° C. to remove resin components and the like therefrom. After this firing process for forming the phosphor layers 9-11, sealing glass frits are applied around the edge of the rear glass substrate 5 to herewith form a sealing glass layer, and calcinated at around 350° C. in order to remove resin components and such from the formed sealing glass layer (frit calcination process).
Then, the front glass substrate 1 and the rear glass substrate 5 are laid on top of each other so that the display electrodes 2 and the address electrodes 6 face at right angles to one another. These superimposed glass substrates are attached and sealed by heating at a temperature (approximately 450° C.) higher than the softening temperature of the sealing glass (sealing process).
Subsequently, as the sealed panel formed of the front and rear glass substrates 1 and 5 is heated up to around 350° C., air is evacuated from the internal space formed between the both glass substrates, i.e. the space which is formed between the front and rear glass substrates 1 and 5, and to which the phosphor layers are exposed (evacuation process) After the evacuation process is completed, discharge gas is introduced to the space until the pressure reaches a predetermined point (normally, 39.9 kPa-66.5 kPa, or 300 Torr-500 Torr).
With such a PDP, there has been a challenge to improve the luminescent characteristics, including the luminance, for example, and to reduce time-lapse changes in luminescent characteristics of the phosphor layers so as to realize an extended quality assurance period.
As to a PDP, in particular, it is sometimes the case that the quality assurance period is determined based on the time-lapse changes in luminescent characteristics of the phosphors used for a luminous display unit of the PDP.
Due, for example, to moisture and application of heat in the PDP manufacturing process, the luminance of phosphors deteriorates and the chromaticity of the phosphors also changes. Thus, the time-lapse changes in phosphors during the PDP manufacturing process leads to degradation of the panel's characteristics. In addition, the phosphor layers are exposed to plasma associated with an electric discharge during the time when the PDP is in operation, which results in further changes in phosphor layers over time. Furthermore, the time-lapse changes in phosphors sometimes lead to deterioration in the PDP's luminescent characteristics over time, which in turn results in the end of the product's life.
This is also the case with a mercury-free fluorescent lamp of which the phosphor layer is excited by vacuum ultraviolet light to emit light. The time-lapse changes in phosphor layer may account for the duration of life.
Under such a circumstance, with light-emitting elements such as a PDP and a mercury-free fluorescent lamp, it is desired to suppress the time-lapse changes in luminescent characteristics of the phosphors caused during the manufacturing process and the time when these light-emitting elements are in operation.
As a technology for suppressing the time-lapse changes in phosphors, a method in which the phosphors are heat-treated (i.e. fired) at a high temperature of approximately 1100° C. to improve the crystallinity is well known.
In addition, in order to suppress deterioration in the phosphor layers, there is a known method in which the surface of phosphor particles is covered with a protective coat made of MgO by using vapor deposition, dipping, sputtering, or spraying techniques as described in Patent Reference 1.
As a method of forming a long lasting phosphor, Patent Reference 2 proposes to supply a coating precursor, e.g. trimethyl aluminum, and mixed gas composed of oxygen and ozone into a reactor vessel, and coat phosphor particles by spending a considerable amount of time.                Patent Reference 1: Japanese Laid-Open Patent Application Publication No. H8-31325        Patent Reference 2: Japanese Laid-Open Patent Application Publication No. 2000-96044        